Body Fat Percentage Calculator

Body fat percentage is the proportion of your total body weight that consists of fat tissue. It's calculated as (Fat Mass ÷ Total Body Weight) × 100. Unlike BMI, which only considers height and weight, body fat percentage directly measures body composition—distinguishing between fat mass and lean mass (muscle, bone, organs, water). This matters because two people with identical BMIs can have vastly different body compositions. Someone with high muscle mass might be classified as 'overweight' by BMI despite having low body fat and excellent health markers. Conversely, someone with 'normal' BMI might carry excess fat with low muscle mass (skinny fat), increasing metabolic disease risk. Body fat percentage provides a more accurate picture of health, fitness, and metabolic risk than weight or BMI alone.

Healthy body fat ranges differ significantly by sex and age. FOR MEN: Essential fat (2-5%) is the minimum for organ function—below this is dangerous. Athletic (6-13%) is typical for competitive athletes with visible abs. Fitness (14-17%) represents a fit, lean appearance. Average (18-24%) is typical for adults without specific training. Above 25% is considered obese with increased health risks. FOR WOMEN: Essential fat (10-13%) is higher than men due to reproductive and hormonal needs. Athletic (14-20%) is typical for female athletes. Fitness (21-24%) represents a fit appearance. Average (25-31%) is typical for adults. Above 32% is considered obese. Women naturally carry more body fat than men—a 'healthy' percentage for women would be classified as 'average to high' for men, and vice versa.

The US Navy method uses circumference measurements and height to estimate body fat percentage through validated regression equations. FOR MEN: Body Fat % = 495 / (1.0324 - 0.19077 × log10(waist - neck) + 0.15456 × log10(height)) - 450. FOR WOMEN: Body Fat % = 495 / (1.29579 - 0.35004 × log10(waist + hip - neck) + 0.22100 × log10(height)) - 450. The formula was developed by the Naval Health Research Center and validated against hydrostatic weighing (underwater weighing). It's considered accurate to within ±3-4% of actual body fat when measurements are taken correctly. The Navy uses this method for fitness standards because it requires only a tape measure and provides consistent, reproducible results across large populations.

Circumference methods like the Navy formula have a standard error of estimate (SEE) of approximately ±3-5% compared to gold standard methods (DEXA, hydrostatic weighing). This means if your calculated body fat is 20%, your actual body fat likely falls between 15-25%. Accuracy depends heavily on: (1) MEASUREMENT TECHNIQUE—consistent landmarks, tape tension, and timing. (2) BODY FAT DISTRIBUTION—formulas assume typical fat distribution patterns. Those with unusual distribution (e.g., very lean limbs but higher abdominal fat) may see larger errors. (3) MUSCLE MASS—very muscular individuals may get overestimates because large necks reduce the waist-neck calculation. For tracking changes over time rather than absolute values, circumference methods work well when measurements are taken consistently. For precise body composition (e.g., contest prep, research), DEXA or hydrostatic weighing is recommended.

FAT MASS: The total weight of adipose (fat) tissue in your body. This includes essential fat (needed for organ function, hormone production, and nervous system insulation) and storage fat (energy reserves stored subcutaneously and around organs). LEAN MASS (also called Fat-Free Mass or FFM): Everything in your body that isn't fat—including skeletal muscle, bone, organs, blood, water, and connective tissue. Lean mass is metabolically active, meaning it burns calories at rest. More lean mass = higher basal metabolic rate. The goal of body recomposition is to decrease fat mass while maintaining or increasing lean mass. This is why body fat percentage is more useful than weight alone—you might stay the same weight while losing fat and gaining muscle, significantly improving body composition and health.

Women naturally carry 6-11% more body fat than men due to biological and hormonal differences: (1) REPRODUCTIVE FUNCTION—Women require higher essential fat for menstruation, pregnancy, and lactation. Body fat below 10-13% can disrupt hormonal cycles and cause amenorrhea (loss of menstrual period). (2) ESTROGEN—The female hormone promotes fat storage, particularly in hips, thighs, and breasts, for evolutionary reproductive purposes. (3) MUSCLE MASS—Men have 20-30% more muscle mass on average due to testosterone, which means a larger portion of male body weight is lean tissue. (4) FAT DISTRIBUTION—Women store more subcutaneous fat (under skin), while men store more visceral fat (around organs)—different health implications. A body fat of 18% in a woman represents athletic fitness, while the same percentage in a man is considered average.

The formula assumes you'll lose only fat (preserving lean mass): Target Weight = Current Lean Mass ÷ (1 - Target Body Fat %). Example: You weigh 180 lbs at 25% body fat. Fat mass = 180 × 0.25 = 45 lbs. Lean mass = 180 - 45 = 135 lbs. To reach 15% body fat: Target weight = 135 ÷ (1 - 0.15) = 135 ÷ 0.85 = 158.8 lbs. Weight to lose = 180 - 158.8 = 21.2 lbs. IMPORTANT CAVEATS: (1) In reality, some lean mass is typically lost during weight loss (10-25% of total weight lost). (2) Very aggressive deficits increase muscle loss. (3) Resistance training and adequate protein (0.7-1g per lb of bodyweight) help preserve muscle. Our calculator performs this projection automatically when you enter your weight and adjust the target slider.

Visible abdominal muscles depend on both low body fat AND developed ab muscles. General guidelines: FOR MEN: Faint abs appear around 15-17%. Defined 'six-pack' typically requires 10-12%. Competition bodybuilders aim for 5-8% for maximum definition. FOR WOMEN: Faint ab lines appear around 18-20%. Defined abs typically require 15-17%. Female fitness competitors may go to 12-15%. Note that genetics play a significant role—some people have more prominent rectus abdominis muscles or favorable fat distribution that makes abs visible at higher body fat percentages. Also, ab visibility isn't necessarily a health goal—body fat below 6% (men) or 14% (women) can be unsustainable and potentially unhealthy long-term. Many people maintain a slightly higher body fat that feels sustainable while still looking fit.

Several methods exist with varying accuracy and accessibility: DEXA SCAN (Dual-Energy X-ray Absorptiometry): Gold standard. Uses low-dose X-rays to measure bone, fat, and lean tissue. Accuracy ±1-2%. Cost: $50-150 per scan. HYDROSTATIC WEIGHING: Underwater weighing based on body density. Very accurate but requires specialized equipment. Accuracy ±1.5-2%. BOD POD (Air Displacement): Measures body volume via air displacement. Similar accuracy to hydrostatic weighing. Easier than underwater testing. SKINFOLD CALIPERS: Measures subcutaneous fat at multiple sites. Accuracy depends heavily on technician skill. ±3-4% when done correctly. BIOELECTRICAL IMPEDANCE (BIA): Estimates body composition via electrical resistance. Found in smart scales. Accuracy ±3-8% depending on hydration. CIRCUMFERENCE METHODS (Navy, etc.): Uses tape measurements. Accuracy ±3-5%. Most accessible—only requires tape measure. For most people, circumference methods provide sufficient accuracy for tracking progress when done consistently.

Not all fat is metabolically equal. VISCERAL FAT: Stored deep in the abdominal cavity around organs (liver, pancreas, intestines). It's metabolically active, releasing inflammatory cytokines and hormones that increase risk of Type 2 diabetes, cardiovascular disease, and metabolic syndrome. Visceral fat correlates strongly with waist circumference—why waist measurement is a health marker. SUBCUTANEOUS FAT: Stored under the skin (thighs, arms, hips). While excess is still unhealthy, it's less metabolically harmful than visceral fat. Women tend to store more subcutaneous fat (especially lower body), which may partly explain their lower cardiovascular disease risk compared to men with similar BMI. Reducing visceral fat through exercise and diet (especially reducing refined carbs and alcohol) significantly improves metabolic health markers even before visible changes in subcutaneous fat occur.

Yes. Very low body fat can cause health problems: FOR MEN (below 5-6%): Hormonal disruption, decreased testosterone, low energy, weakened immune system, loss of libido. This level is typically only seen in bodybuilders during competition—and is not sustainable. FOR WOMEN (below 12-14%): Hormonal disruption, amenorrhea (loss of menstrual period), decreased bone density (osteoporosis risk), fertility problems, low energy. Female Athlete Triad is a recognized condition combining low energy availability, menstrual dysfunction, and low bone density. Additionally, the METHODS used to achieve very low body fat matter: extreme caloric restriction, overtraining, and dehydration used for rapid fat loss can cause metabolic damage, muscle loss, and psychological issues (eating disorders). Sustainable, moderate body fat levels are healthier long-term than extreme leanness achieved through unhealthy means.

Safe fat loss rates depend on starting body fat and lean mass: HIGHER BODY FAT (>25% men, >32% women): Can safely lose 1-1.5% of body weight per week (1.5-2 lbs for a 200 lb person). Body has ample fat reserves to tap. MODERATE BODY FAT (15-25% men, 25-32% women): Aim for 0.5-1% of body weight per week. Slower rate helps preserve muscle. LOWER BODY FAT (<15% men, <25% women): 0.25-0.5% per week maximum. Aggressive deficits at lower body fat cause disproportionate muscle loss. The leaner you are, the slower you should cut. General rule: A caloric deficit of 500-750 calories/day produces roughly 1-1.5 lbs of fat loss per week. Combine this with resistance training and adequate protein (0.7-1g per lb bodyweight) to maximize muscle retention. Very rapid weight loss typically includes significant water and muscle loss—not pure fat.

Bioelectrical impedance analysis (BIA) scales send a small electrical current through your body. Fat resists current more than lean tissue, allowing body fat estimation. PROS: Convenient, inexpensive, quick, tracks trends over time. CONS: Accuracy varies widely (±3-8%). Readings are highly affected by hydration, food intake, exercise, and time of day. The same person can get body fat readings differing by 5%+ on the same scale within hours. BEST PRACTICES: (1) Measure at the same time daily (morning, after bathroom, before eating). (2) Stay consistent with hydration. (3) Focus on trends over weeks/months, not individual readings. (4) Don't compare readings between different scales. BIA can be useful for tracking relative changes (am I trending up or down?) but shouldn't be trusted for absolute body fat percentage. Circumference methods may actually be more consistent when done carefully.

Body fat tends to increase with age, even at stable weight, due to several factors: (1) MUSCLE LOSS (sarcopenia): Adults lose 3-8% of muscle mass per decade after 30 if not actively training. Less muscle means a higher proportion of body weight is fat. (2) HORMONAL CHANGES: Declining testosterone (men) and estrogen (women after menopause) affect fat distribution and muscle maintenance. (3) METABOLIC SLOWDOWN: Basal metabolic rate decreases with age and muscle loss, making fat gain easier. (4) ACTIVITY REDUCTION: Most people become less active with age. Practical implications: A 50-year-old at the same body fat percentage as a 25-year-old is actually doing relatively better in terms of age-adjusted fitness. Body fat standards are sometimes age-adjusted for this reason. The good news: Resistance training and adequate protein can dramatically slow muscle loss and metabolic decline, maintaining leaner body composition into older age.

No. This body fat calculator runs entirely in your browser. Your measurements, weight, and body composition data are processed locally on your device and are never sent to our servers or stored anywhere. When you close or refresh the page, all data is cleared. Your body composition information stays completely private.